In Vitro Testing of Voltage Indicators: Archon1, ArcLightD, ASAP1, ASAP2s, ASAP3b, Bongwoori-Pos6, BeRST1, FlicR1 and Chi-VSFP-Butterfly

Abstract

Genetically encoded voltage indicators (GEVIs) could potentially be used for mapping neural circuits at the plane of synaptic potentials and plateau potentials – two blind spots of GCaMP-based imaging. In the last year alone, several laboratories reported significant breakthroughs in the quality of GEVIs and efficacy of the voltage imaging equipment. One major obstacle of using well-performing GEVIs in the pursuit of interesting biological data is the process of transferring GEVIs between laboratories, as their reported qualities (e.g. membrane targeting, brightness, sensitivity, optical signal quality, etc.) are often difficult to reproduce outside of the laboratory of the GEVI origin. We have tested eight available GEVIs (Archon1, ArcLightD, ASAP1, ASAP2s, ASAP3b, Bongwoori-Pos6, FlicR1, & chi-VSFP-Butterfly) and two voltage sensitive dyes (BeRST1 & di-4-ANEPPS). We used the same microscope, lens and optical detector, while the light sources were interchanged. GEVI voltage imaging was attempted in three preparations: [1] cultured neurons, [2] HEK293 cells, and [3] mouse brain slices. Systematic measurements were successful only in HEK293 cells and brain slices. Despite the significant differences in brightness and dynamic response (ON rate), all tested indicators produced reasonable optical signals in brain slices and solid in vitro quality properties, in the range initially reported by the creator laboratories. Side-by-side comparisons between GEVIs and organic dyes obtained in HEK293 cells and brain slices by a “third party” (current data), will be useful for determining the right voltage indicator for a given research application.

Significance Statement

Voltage indicators are useful for studying brain circuitry and brain information processing, as they detect subthreshold neuronal signals missed by calcium indicators. But which voltage indicator should one use when planning a new (expensive) project? We performed systematic side-by-side testing of several popular genetically encoded voltage indicators (GEVIs), and then a voltage sensitive dye was used in the same test. All reported measurements were acquired on the same electrophysiology-imaging station, using the same optical path and detector. Our results are potentially useful for guiding the practical choice of a GEVI indicator. We describe available excitation wavelengths, emission wavelengths, brightness, voltage-sensitivity, and signal-to-noise ratio.